1. Field of the Invention
The present invention relates to a magnetoresistance effect element suitable for use in, for example, a reproducing magnetic head and a high sensitivity magnetic sensor.
2. Description of the Related Art
With increase in a magnetic recording density, demands for improvement in the sensitivity of a magnetic head are on a sharp increase, and vigorous researches are being made in an attempt to develop a magnetic head utilizing a magnetoresistance effect.
The conventional magnetic head mainly utilizes a ferromagnetic magnetoresistance effect and includes, for example, an Fe--Ni permalloy thin film. However, the magnetoresistance ratio, i.e., (p.sub.1 -p.sub.t)/p.sub.0 .times.100, where p.sub.1 is the electric resistance in a direction parallel with the direction of magnetization, p.sub.t is the electric resistance in a direction perpendicular to the direction of magnetization, and p.sub.0 is the electric resistance under a zero magnetic field, is only about 2% in the conventional magnetic head utilizing the magnetoresistance effect.
A magnetoresistance effect element comprising magnetic layers positioned to face each other with a nonmagnetic intermediate metal layer interposed therebetween is proposed in, for example, Japanese Patent Disclosure (Kokai) No. 2-61572. A magnetoresistance effect is obtained in this element by applying a magnetic field to the element so as to change the relative directions of the magnetic spins between the magnetic layers. The element basically utilizes the scattering of electrons, said scattering being dependent on the direction of spin generated at the interface between the magnetic layer and the intermediate layer, with the result that the thickness of the intermediate layer is made smaller than the mean free path of the electron.
However, the magnetoresistance effect element of the construction described above has a low resistivity, with the result that a high current density is required for obtaining a sufficient signal output. It follows that problems such as heat generation and electromigration are brought about, and reliability and durability of the element are insufficient.
A magnetoresistance effect element utilizing a magnetic tunneling junction is disclosed in, for example, Japanese Patent Disclosure No. 4-42417, Japanese Patent Disclosure (Kokai) No. 4-103013 and Japanese Patent Disclosure (Kokai) No. 4-103014. The element of this type comprises magnetic layers positioned to face each other with a very thin insulating film, i.e., about 10.ANG. thick, interposed therebetween, and utilizes a change in tunnel conductance brought about by the relative angles of magnetizations of the magnetic layers.
The magnetoresistance effect element utilizing the magnetic tunneling junction has a small tunnel conductance, making it possible to obtain an output signal with a relatively low current density. Thus, problems such as heat generation and electromigration are unlikely to take place. However, it is necessary to form satisfactorily a very thin insulating film free from defects such as pin holes in manufacturing the element of this type. It is difficult to apply the element of this type to commercial manufacture, since the problems in terms of reproducibility, durability, stability, etc. are generated.
Also proposed is a magnetoresistance effect element having Fe/Ge/Co junction as a magnetic tunneling junction, as described in "Phys. Lett. 54A, 225 (1975)". In this element, however, the spin information of carriers of the magnetic layer within the semiconductor layer is lost when a tunneling current detects and reliability problem occurs if the intrinsic semiconductor layer of the Ge layer is formed thick. In other words, the element performs a desired function only when the Ge layer is formed very thin. It is also necessary to form an insulating layer acting as a barrier layer between the Ge layer and the magnetic Fe layer and between the Ge layer and the magnetic Co layer. What should be noted is that it is impossible to control the barrier height.
As described above, the magnetoresistance effect element utilizing a magnetic tunneling junction and the spin information of the carrier within the magnetic layer is highly useful in industries. However, various problems must be solved before the element is put to a practical use.